ugh... the friendly fire discussion is wearing out.
Yes, their will always be friendly fire:
1. from the ground to the air.
2. from the air to the ground.
3. from the air to the air.
4. from the ground to the ground.
My point is simply that in a modern air force tactical air power has reached a point that friendlies are infrequently, accidentally killed. Note that I said friendlies, yes we accidentally bomb the wrong building, farm, mosque, 7/11 or even the wrong country

, whatever. But we rarely bomb our own guys in uniform. You can comb the internet all day long but the numbers don't add up. The USAF/coalition has basically been flying non-stop since Sept. 11 2001 and we only have a handful of accidents.
Also, the type of friendly fire
I'm referring to is the completely absurd and atrocious type "Lets shoot at vehicles when the enemy does not have any in the whole country" type. For instance Soviet incursion into Afghanistan. Mujahideen forces had minimal if any vehicles but try telling that the Su-25 pilots when your totally sweet Spetsnaz mech column goes up in flames.
As for Flak/AAA attacking friendlies. The original comment by JohnHale pertained to WINSPWW2. Which would make sense because (to my knowledge) those systems did not have IFF interrogation systems. They just had the Mark I eyeball.
Flak/AAA friendly fire in the present tense is hard to judge. So many nations purchased a complete IADS system from Russia that it would be very difficult to determine how reliable the IFF is. There's just so many factors to account for, most of which are well beyond the scope of this game. Lets put it this way, if I were a pilot in one of those countries with the old Russian systems, I would be nervous.